The invention relates to a dipole exciter for an antenna with parabolic reflector for transmitting electromagnetic waves, consisting of a rigid co-axial line fastened at one end to the reflector and having an inner conductor, an outer conductor concentrically surrounding said inner conductor with dielectric contained between the two conductors, in which connection a dipole connected in electrically conductive manner with the outer conductor is arranged on the free end of the conductor lying approximately at the focal point of the reflector, two axially extending slots which lie diametrically opposite each other being arranged in the outer conductor within the region of the dipole, and inner and outer conductors being short-circuited at a narrowly limited place in circumferential direction in the region of the slots (U.S. book by S. Silver, "Microwave Antenna Theory and Design", 1949, McGraw-Hill).
Such an exciter is used, for instance, for the illuminating of directional antennas with parabolic reflectors for radio direction finding, satellite communications or radio location. For the direct illuminating of the reflector it is arranged approximately at the focal point thereof. "Illuminating" in this connection comprises both directions of transmission of the electromagnetic waves and therefore the waves to be sent out and those to be received.
In the known dipole exciter according to the aforementioned U.S. book, the dipole consists of two bars which protrude in radial direction from the outer conductor of the co-axial line. By the short-circuit between inner conductor and outer conductor, the line is made symmetric at the end. By this measure in cooperation also with the slots in the outer conductor the dipole can be placed in oscillation. This known dipole exciter is limited to a relatively narrow frequency band with respect to the electromagnetic waves to be transmitted. It is used, for instance, for the region of 1.7 to 1.9 GHz, and therefore a bandwidth of 200 MHz. Upon a widening of the frequency range, such high reflections result from the superimposing of return waves that the signals to be transmitted are falsified. For different frequency ranges therefore, a relatively large number of different dipoles exciters must be manufactured and possibly kept in stock.